<canvas #canvas width="200" height="150" style="border: 1px dashed gray;"></canvas>
<canvas #canvas2 width="200" height="150" style="border: 1px dashed gray;"></canvas>
<canvas #canvas3 width="200" height="150" style="border: 1px dashed gray;"></canvas>
<br>
<canvas #canvas4 width="200" height="150" style="border: 1px dashed gray;"></canvas>
<canvas #canvas5 width="200" height="150" style="border: 1px dashed gray;"></canvas>
<canvas #canvas6 width="200" height="150" style="border: 1px dashed gray;"></canvas>
<br>
<canvas #canvas7 width="200" height="150" style="border: 1px dashed gray;"></canvas>
<canvas #canvas8 width="200" height="150" style="border: 1px dashed gray;"></canvas>
<br>
<canvas #canvas9 width="200" height="150" style="border: 1px dashed gray;"></canvas>
<button (click)="beforeClearCanvas()">绘制</button>
<button (click)="clearCanvas(canvas9)">清空canvas</button>
